The Repository @ St. Cloud State

Open Access Knowledge and Scholarship

Date of Award


Culminating Project Type


Degree Name

Biological Sciences - Cell and Molecular: M.S.




College of Science and Engineering

First Advisor

Heiko Schoenfuss

Second Advisor

Satomi Kohno

Third Advisor

Stephanie Hummel

Fourth Advisor

Michael Ernst

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

Keywords and Subject Headings

Complex mixtures, multi-generational, fathead minnows, life-cycle, environmental, nitrate


More than one-third of the Earth’s freshwater is used for agricultural, industrial, and domestic purposes leading to the frequent co-occurrence of nitrate and mixtures of contaminants of emerging concerns in aquatic ecosystems. However, little is understood about the consequences of life-cycle exposure of fishes to these complex environmental mixtures. This project examined changes in physiology, performance, and reproduction in fathead minnows across three generations of exposure to agricultural and urban mixtures at environmentally relevant concentrations with an added stressor of nitrate. Exposure of adult fathead minnows in the first, but not second, generation to high nitrate concentrations resulted in a two-fold increase in egg production. In the second generation, the agricultural mixture enhanced fecundity in female fathead minnows above levels observed in EtOH control fish. Contrary to some published studies, neither nitrate nor estrogenic agricultural mixtures stimulated vitellogenin production in male fishes. In contrast, feminization (presence of the egg-yolk protein vitellogenin) was found in first generation males following exposure only to an urban chemical mixture independent of nitrate concentrations. Adult behavior does not appear to be affected regardless of treatment and generation. In contrast, larval behaviors, including predator avoidance performance and foraging efficiency, were both improved in higher nitrate treatments. Using an extended life-cycle fathead minnow exposure, we were able to improve our understanding of the consequences associated with long-term exposures to complex environmental mixtures. Overall, the observed effects of environmentally realistic mixtures were subtle and did neither follow a clear dose-response or matched effects observed in single compound exposures in the published literature. The complexity of interactions between multiple pollutant stressors observed in the current study highlight the need for additional such studies to ensure adequate assessment of environmental risk.


For my parents, James and Denise King, without whom none of this would have been possible, thank you for instilling in me the value of knowledge, and always supporting my dreams and aspirations

For my grandparents, Bruce and Cheri Horne, who inspired me through his actions and lessons, and taught me I could both work and pursue my passions simultaneously.

For my best friends, Bekah Patino, Logan Andersen, Kalli Beaulieu, and Charles Christen, who supported me and gave me the motivation to pursue my dreams. Thank you for the encouragement.

For my advisor and mentor, Heiko L. Schoenfuss, thank you for providing me with the support, guidance, and encouragement necessary to complete this project.

Planning, research, execution, and analysis of chapter 2 was conducted in collaboration with, James Gerads1, Charles Christen1, Yasmeena Thabet1, Satomi Kohno1, Nicholas Cipoletti1, Stephanie Hummel2, Edward Furlong3, Leslie Kanagy3, and Heiko L. Schoenfuss1 who will be identified as co-authors in a planned manuscript. This work was supported by funding from the Great Lakes Restoration Initiative through the U.S. Fish and Wildlife Service’s CEC Team [F15AC00124; to HLS], 2019 Society of Environmental Toxicology and Chemistry travel grant [CKK], and 2019 St. Cloud State University travel grant [CKK].

1 St. Cloud State University, Aquatic Toxicology Laboratory, St. Cloud, MN

2 U.S. Fish and Wildlife Service, Bloomington, MN

3 U.S. Geological Survey, National Water Quality Laboratory, Denver, CO



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.